The term “stretch bonded laminate” refers to a composite elastic material made according to a stretch bonding lamination process, i.e., elastic layer(s) are joined together with additional facing layers when only the elastic layer is in an extended condition (such as by at least about 25 percent of its relaxed length) so that upon relaxation of the layers, the additional layer(s) is/are gathered. Such laminates usually have machine directional (MD) stretch properties and may be subsequently stretched to the extent that the additional (typically non-elastic) material gathered between the bond locations allows the elastic material to elongate. One type of stretch bonded laminate is disclosed, for example, by U.S. Pat. No. 4,720,415 to Vander Wielen et al., in which multiple layers of the same polymer produced from multiple banks of extruders are used. Other composite elastic materials are disclosed in U.S. Pat. No. 5,385,775 to Wright and copending U.S. Patent Publication No. 2002-0104608, published 8 Aug. 2002, each of which is incorporated by reference herein in its entirety. Such stretch bonded laminates may include an elastic component that is a web, such as a meltblown web, a film, an array/series of generally parallel continuous filament strands (either extruded or pre-formed), or a combination of such. The elastic layer is bonded in a stretched condition to two inelastic or extendable nonwoven facing materials, such that the resulting laminate is imparted with a textural feel that is pleasing on the hand. In particular, the elastic layer is bonded between the two facing layers, such that the facing layers sandwich the elastic layer. In some instances, the gatherable facing layers may also be necked, such that the stretch bonded laminate is actually a necked stretch bonded laminate that may have some extension/elasticity in the cross-machine direction (CD).
To “neck” or “necked” refers to a process of tensioning a fabric in a particular direction thereby reducing the width dimension of the fabric in the direction perpendicular to the direction of tension. For example, tensioning a nonwoven fabric in the MD causes the fabric to “neck” or narrow in the CD and give the necked fabric CD stretchability. Examples of such extensible and/or elastic fabrics include, but are not limited to, those described in U.S. Pat. No. 4,965,122 to Morman et al. and U.S. Pat. No. 5,336,545 to Morman et al. each of which is incorporated herein by reference in its entirety.
“Neck bonding” refers to the process wherein an elastic member is bonded to a non-elastic member while only the non-elastic member is extended or necked so as to reduce its dimension in the direction orthogonal to the extension. “Neck bonded laminate” refers to a composite elastic material made according to the neck bonding process, i.e., the layers are joined together when only the non-elastic layer is in an extended/necked condition. Such laminates usually have cross directional stretch properties. Further examples of neck-bonded laminates are such as those described in U.S. Pat. Nos. 5,226,992, 4,981,747 to Morman and U.S. Pat. No. 5,514,470 to Haffner et al., each of which is incorporated by reference herein in its entirety.
“Neck-stretch bonding” generally refers to a process wherein an elastic member is bonded to another member while the elastic member is extended (such as by about 25 percent of its relaxed length) and the other layer is a necked, non-elastic layer. “Neck-stretch bonded laminate” refers to a composite elastic material made according to the neck-stretch bonding process, i.e., the layers are joined together when both layers are in an extended condition and then allowed to relax. Such laminates usually have multi-directional stretch properties.
Such stretch bonded laminates may be used to provide elasticity to various components of a personal care product and with the added benefit of a pleasant fabric-like touch, such as a diaper liner or outercover, diaper waist band material, diaper leg gasketing (cuff) material, diaper ear portions (that is, the point of attachment of a fastening system to a diaper), as well as side panel materials for diapers and child training pants. Since such materials often come in contact with skin of a human body, it is desirable that such materials be relatively soft to the touch, rather than rubbery in their feel (a sensation common for elastic materials). Such materials may likewise provide elasticity and comfort for materials that are incorporated into protective workwear, such as surgical gowns, face masks and drapes, labcoats, or protective outercovers, such as car, grill or boat covers.
While such soft and stretchy materials have assisted in making such elastic materials more user-friendly, there is still a need for such products that provide even more of a cloth-like fabric feel. In this regard, there is a need for such materials that provide even higher levels of gathering. Further, there is a need for such laminate products with even greater flexibility as a result of reduced overall basis weight. There is likewise a need for a laminate material that provides reduced stiffness as a result of the elimination of one facing layer on the laminate and the use of lower basis weight elastic layer components. Such a laminate would be more efficient in its use as an elastic material, plus the elimination of one facing layer would be cost-effective. Such a laminate could provide ease of use/extension, with better ability to retract since there would be no drag of extra facing layers. Essentially, such a laminate would provide for higher levels of retraction with lower weights of polymer. However, even with all of these perceived benefits, to date a single sided stretch bonded laminate (that is a stretch bonded laminate with a gatherable facing layer on only one side) has been elusive because of manufacturing challenges.
In utilizing stretch bonded laminates that themselves incorporate an adhesive component, it has been desirable to select adhesives that do not add to the stiffness of the material. Such stiffness has a negative impact on the overall feel of the product and the ability of the product to provide stretch attributes when in use. It therefore would be desirable to develop additional adhesive arrangements that would not negatively impact laminate material feel and performance, while still allowing for the formation of a single sided material.
Many adhesives are typically somewhat elastic themselves, and tend to retain some level of tackiness even after they are dried or cured. As a result, because of their inherent tackiness, it has been necessary, at least with respect to filament, film, and web based stretch bonded laminates, to utilize facings on both sides of the center elastic component (i.e. filament array), so as to avoid roll blocking during processing/storage. For the purposes of this application, the terms “roll blocking” and “roll sticking” shall be used interchangeably, and shall refer to the propensity of tacky films, tacky filament arrays or other tacky sheet materials to stick to themselves upon being rolled up for storage, prior to final use. Such roll blocking may prevent use of the material contained on a roll as a result of the inability to unwind such rolled material when it is actually needed. In filament-based stretch bonded laminates, adhesive is often applied to the facing layers themselves, and then the facing layers are combined in a nip with the filament array between them. Such an arrangement may generally be described as an ABA laminate, where A is a facing layer and B is an elastic layer.
While it would be desirable to reduce the basis weight of the stretch bonded laminate such that the material is less costly and more flexible, it has been heretofore unclear how to eliminate the extra facing layer(s) without causing the rolled material to stick, if it is to be stored prior to use. It is therefore desirable to have a single sided stretch-bonded laminate that demonstrates acceptable elastic performance, but that is also capable of being stored on a roll without concern for roll blocking. It is also desirable to have a material that may be maintained on a roll under acceptable storage conditions, such as for a given period of time, and at a range of temperatures. It is to such needs that the current invention is directed.